U.S. patent application number 10/500845 was filed with the patent office on 2005-10-20 for sample retainer for x-ray fluorescence analysis, x-ray fluorescence analyzing method using the same and x-ray fluorescence spectrometer therefor.
Invention is credited to Inoue, Michiko, Moriyama, Takao.
Application Number | 20050232393 10/500845 |
Document ID | / |
Family ID | 34113861 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050232393 |
Kind Code |
A1 |
Moriyama, Takao ; et
al. |
October 20, 2005 |
SAMPLE RETAINER FOR X-RAY FLUORESCENCE ANALYSIS, X-RAY FLUORESCENCE
ANALYZING METHOD USING THE SAME AND X-RAY FLUORESCENCE SPECTROMETER
THEREFOR
Abstract
To provide a sample retainer for X-ray fluorescence analysis,
which is used in pretreating a liquid sample and then in X-ray
fluorescence analysis of contents of such liquid sample, can
sufficiently improve the limit of detection by suppressing the
background and, also, allowing the fluorescent X-rays of a high
intensity to be emitted uniformly, the sample retainer 5 comprises
a ring-shaped pedestal 2; a hydrophobic film 3 of a thickness
smaller than 10 .mu.m and having a peripheral portion 3a held by
the pedestal and also having a transmitting portion 3b for passage
of X-rays therethrough; and a sheet-like liquid absorbent element 4
applied to the transmitting portion 3b of the hydrophobic film 3
and having a thickness within the range of 1 to 100 .mu.m; wherein
a liquid sample 1 is adapted to be dispensed dropwise onto and
dried on the liquid absorbent element 4b with contents of the
liquid sample 1 consequently retained thereon.
Inventors: |
Moriyama, Takao; (Osaka,
JP) ; Inoue, Michiko; (Osaka, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
34113861 |
Appl. No.: |
10/500845 |
Filed: |
July 7, 2004 |
PCT Filed: |
March 31, 2004 |
PCT NO: |
PCT/JP04/04736 |
Current U.S.
Class: |
378/47 |
Current CPC
Class: |
G01N 2223/076 20130101;
G01N 23/223 20130101 |
Class at
Publication: |
378/047 |
International
Class: |
G01T 001/36; G01N
023/223 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2003 |
JP |
2003-285041 |
Claims
What is claimed is:
1. A sample retainer for X-ray fluorescence analysis for use in
pretreating a liquid sample and then in X-ray fluorescence analysis
of contents of such liquid sample, which retainer comprises a
ring-shaped pedestal; a hydrophobic film of a thickness smaller
than 10 .mu.m and having a peripheral portion held by the pedestal
and also having a transmitting portion for passage of X-rays
therethrough; and a sheet-like liquid absorbent element applied to
the transmitting portion of the hydrophobic film and having a
thickness within the range of 1 to 100 .mu.m; wherein a liquid
sample is adapted to be dispensed dropwise onto and dried on the
liquid absorbent element with contents of the liquid sample
consequently retained thereon.
2. The sample retainer for X-ray fluorescence analysis as claimed
in claim 1; wherein the hydrophobic film is made of a material
selected from the group consisting of polyester, polypropylene and
polyimide; and wherein the liquid absorption element is made of
paper.
3. The sample retainer for X-ray fluorescence analysis as claimed
in claim 2; wherein the liquid absorption element is made of paper
containing a porous powder.
4. An X-ray fluorescence analyzing method utilizing the sample
retainer for X-ray fluorescence analysis as defined in claim 1,
which method comprises: causing a liquid sample to be dispensed
dropwise onto and dried on a liquid absorption element with
contents of the liquid sample consequently retained thereon;
irradiating an area of the liquid absorption element with primary
X-rays, to thereby measure an intensity of secondary X-rays
generated.
5. An X-ray fluorescence spectrometer utilizing the sample retainer
for the X-ray fluorescence analysis as defined in claim 1, which
spectrometer comprises: a source of X-rays for irradiating an area
of a liquid absorption element, where a liquid sample is dispensed
dropwise onto and dried on the liquid absorption element with
contents of the liquid sample consequently retained thereon; and a
detecting device for measuring the intensity of the secondary
X-rays emitted from that area of the liquid absorption element.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a sample retainer for X-ray
fluorescence analysis, which is used in pretreating a liquid sample
and then in X-ray fluorescence analysis of contents of such liquid
sample, an X-ray fluorescence analyzing method of utilizing such
sample retainer and an X-ray fluorescence spectrometer
therefore.
[0003] 2. Description of the Prior Art
[0004] Hitherto, as a technique to perform X-ray fluorescence
analysis for pretreating a liquid sample and analyzing contents
contained in such liquid sample, a filter paper drop method
(micro-droplet method) is known, in which the liquid sample is
dispensed dropwise onto and dried on a filter paper so that the
liquid sample can be not only concentrated, but also retained on
such filter paper. However, since the filter paper has a thickness
of a few hundred micrometer, scattered X-rays of the primary X-rays
occurs considerable, resulting in increase of the background. Also,
considering the liquid absorption capacity of the filter paper,
only 50 to 100 microliter of the liquid sample can be dispensed
dropwise at a time and, in the case of a trace quantity of
contents, the intensity of fluorescent X-rays which will be emitted
from contents concentrated on the filter paper and will
subsequently be sensed by a detector may not be insufficient even
though dropwise dispense and drying are repeated a number of times
before the filter paper is excessively deformed. In other words,
the gradient of the calibration curve (a constant associated with
the fluorescent X-ray intensity, which is used in the equation of
the calibration curve indicative of the concentration of the
contents in the liquid sample) does not decrease sufficiently.
Accordingly, the limit of detection (LLD) shown in the following
equations is, for example, about a few hundred ppb in a region of
heavy elements required in environmental analysis and cannot be
regarded sufficient.
LLD=3.times.b.times..sigma..sub.BG (1)
.sigma..sub.BG=(I.sub.BG/(1000.times.t)).sup.1/2 (2)
[0005] wherein b represents the gradient of the calibration curve,
IBG represents the intensity (kcps) of the background X-rays and t
represents the length of measurement time (second).
[0006] Accordingly, in order to improve the limit of detection
within the bounds of the limited length of measurement time and,
also, within the bounds of constant applied voltage and current,
there are two ways available, in which the contents of the liquid
sample are concentrated so that the sensitivity can increased to
thereby improve the gradient of the calibration curve (i.e., to
minimize the value of the gradient of the calibration curve. In
other words, the contents are concentrated as much as possible so
that the fluorescent X-rays emitted therefrom and subsequently
sensed by the detector can be increased.) and in which the
intensity of the background X-rays is minimized, respectively.
[0007] In order to improve the limit of detection based on these,
there is a technique in which a polymer film of about 0.5 .mu.m in
thickness is formed with a vapor deposited film of, for example,
carbon so that a liquid sample can be dispensed dropwise onto and
subsequently dried on the area of the polymer film, where the vapor
deposited film has been formed, so that contents of the liquid
sample can be retained thereon. (See the Japanese Laid-open Patent
Publication No. 2003-90810.)
[0008] However, since the vapor deposited film is extremely thin
and has its diameter limited to about 2 mm in order for the liquid
sample to be uniformly concentrated, the amount of the liquid
sample that can be dispensed dropwise at a time is equal to or
smaller than the amount that can be dispensed dropwise onto the
filter paper. Accordingly, although the background can be reduced
by the utilization of the polymer film and the vapor deposited film
smaller in thickness than the filter paper, the intensity of the
fluorescent X-rays that can be obtained does not increase and,
therefore, improvement of the limit of detection is not sufficient.
Also, with a small surface area of the vapor deposited film, even
though dropwise dispensing and drying are repeated to concentrate a
large amount of the contents, there are possibilities that the
liquid sample cannot be retained stably and that the background
will increase as a result of emission of a large amount of
scattered X-rays as a result of crystallization of the contents. It
is to be noted that if the surface area of the vapor deposited film
is increased in order to increase the amount to be dispensed
dropwise so that the intensity of the fluorescent X-rays can be
increased, concentration will become uneven and emission of the
fluorescent X-rays will then become uneven and unstable. (Paragraph
0019 in the previously mentioned publication.)
SUMMARY OF THE INVENTION
[0009] The present invention has been devised with the foregoing
problems taken into consideration and is intended to provide what,
in a sample retainer for X-ray fluorescence analysis, which is used
in pretreating a liquid sample and then in X-ray fluorescence
analysis of contents of such liquid sample, an X-ray fluorescence
analyzing method utilizing such sample retainer and an X-ray
fluorescence spectrometer therefore, can sufficiently improve the
limit of detection by suppressing the background and, also,
allowing the fluorescent X-rays of a high intensity to be emitted
uniformly.
[0010] In order to accomplish the foregoing object, the sample
retainer for X-ray fluorescence analysis according to a first
aspect of the present invention is for use in pretreating a liquid
sample and then in X-ray fluorescence analysis of contents of such
liquid sample, and includes a ring-shaped pedestal, a hydrophobic
film of a thickness smaller than 10 .mu.m and having a peripheral
portion held by the pedestal and also having a transmitting portion
for passage of X-rays therethrough, and a sheet-like liquid
absorbent element applied to the transmitting portion of the
hydrophobic film and having a thickness within the range of 1 to
100 .mu.m; wherein a liquid sample is adapted to be dispensed
dropwise onto and dried on the liquid absorbent element with
contents of the liquid sample consequently retained thereon.
[0011] According to this first aspect of the present invention, in
the first place, since the hydrophobic film and the liquid
absorption element, that are irradiated with primary X-rays, have a
sufficiently small thickness, it is possible to decrease the
scattered X-rays to thereby suppress the background. On the other
hand, since with the liquid absorbent element having a proper
thickness and applied to the hydrophobic film, a sufficient amount
of the liquid sample can be retained and can be uniformly
concentrated, it is possible to generate uniformly the fluorescent
X-rays of a high intensity. Accordingly, the detection limit can be
sufficiently improved.
[0012] In this first aspect of the present invention, the use is
preferred of polyester (for example, polyethylene terephthalate),
polypropylene or polyimide for the hydrophobic film and paper can
be used for the liquid absorption element and, in addition, the use
is preferred of a paper containing a porous powder, for example,
talcum powder (a powder of talc).
[0013] The X-ray fluorescence analyzing method according to a
second aspect of the present invention makes use of the sample
retainer for the X-ray fluorescence analysis according to the first
aspect of the present invention and includes causing a liquid
sample to be dispensed dropwise onto and dried on the liquid
absorption element so that contents of the liquid sample can be
retained thereon, irradiating an area of the liquid absorption
element with primary X-rays so that generated secondary X-rays can
be measured.
[0014] The X-ray fluorescence spectrometer according to a third
aspect of the present invention makes use of the sample retainer
for the X-ray fluorescence analysis according to the first aspect
of the present invention and includes a source of X-rays for
irradiating an area of the liquid absorption element, where the
liquid sample is dispensed dropwise onto and dried on the liquid
absorption element with contents of the liquid sample consequently
retained thereon, and a detecting device for measuring the
intensity of the secondary X-rays emitted from that area of the
liquid absorption element.
[0015] According to the second and third aspects of the present
invention, since the sample retainer for the X-ray fluorescence
analysis according to the first aspect of the present invention is
utilized, function and effects similar to those in the first aspect
of the present invention can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In any event, the present invention will become more clearly
understood from the following description of preferred embodiments
thereof, when taken in conjunction with the accompanying drawings.
However, the embodiments and the drawings are given only for the
purpose of illustration and explanation, and are not to be taken as
limiting the scope of the present invention in any way whatsoever,
which scope is to be determined by the appended claims. In the
accompanying drawings, like reference numerals are used to denote
like parts throughout the several views, and:
[0017] FIG. 1 is a perspective view of a sample retainer for the
X-ray fluorescence analysis, which is a first embodiment of the
present invention;
[0018] FIG. 2 is a perspective view showing a liquid sample being
dispensed dropwise onto the sample retainer;
[0019] FIG. 3 is a longitudinal sectional view of the sample
retainer;
[0020] FIG. 4 is a graph showing comparison between a qualitative
spectrum resulting from analysis, conducted with the use of the
sample retainer, and a qualitative spectrum resulting from analysis
conducted with the use of the conventional filter paper;
[0021] FIG. 5 is a schematic diagram showing an X-ray fluorescence
spectrometer according to a third embodiment of the present
invention, which is used in the practice of the X-ray fluorescence
analyzing method according to a second embodiment of the present
invention;
[0022] FIG. 6 is a longitudinal sectional view showing a
modification of a method of placing the sample retainer on a sample
stage;
[0023] FIG. 7 is a longitudinal sectional view showing a different
modification of the method of placing the sample retainer on the
sample stage; and
[0024] FIG. 8 is a longitudinal sectional view showing a further
modification of the method of placing the sample retainer on the
sample stage.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0025] In the first place, a sample retainer for the X-ray
fluorescence analysis which is a first embodiment of the present
invention will be described. This sample retainer is used in
pretreating a liquid sample and then in X-ray fluorescence analysis
of contents of such liquid sample and includes, as shown in FIG. 1,
a ring-shaped pedestal 2 for stably holding a hydrophobic film and
made of a resinous material such as, for example, polyethylene or
polystyrene, the hydrophobic film 3 of a thickness smaller than 10
.mu.m and having a peripheral portion 3 held by the pedestal 2 and
also having a transmitting portion 3b for passage of X-rays
therethrough, and a sheet-like liquid absorbent element 4 applied
to the transmitting portion 3b of the hydrophobic film and having a
thickness within the range of 1 to 100 .mu.m, wherein by causing a
liquid sample to be dispensed dropwise onto and dried on the liquid
absorbent element 4, contents of the liquid sample can be
concentrated and retained.
[0026] Referring now to FIG. 3 showing a longitudinal sectional
view, the hydrophobic film 3 is prepared from polyethylene
terephthalate having a thickness of 1.5 .mu.m and is of a round
shape having a diameter substantially equal to the outer diameter
of the pedestal 2 (for the purpose of illustration and facilitating
a better understanding, shown on a reduced scale), with the
peripheral portion 3a retained in tight contact with the pedestal
2. A portion of the hydrophobic film 3 other than the peripheral
portion 3a is the transmitting portion 3b for passage of X-rays
therethrough. In FIG. 1 and FIG. 2 as will be mentioned later,
although an inner perimeter of the pedestal 3 is shown by the
broken line as it is hidden beneath the hydrophobic film 3, in
reality it is diaphanous and, therefore, viewable. Also, the liquid
absorption element 4 is prepared from paper of a few .mu.m in
thickness and containing talcum powder as is the case with, for
example, a cosmetic grease-absorbing paper and is of a round shape
of 1.8 cm in diameter and pasted to a center portion of the
hydrophobic film 3 by means of a spray adhesive (the composition of
which contains acrylic rubber (10%), an organic solvent (54%) and
an isohexane gas (36%), with dimethyl ether used as a high pressure
gas for spraying) sprayed to the backside of the liquid absorption
element 4. The bonding agent used for pasting may not be always
limited to the spray adhesive, but any bonding agent can be
employed, provided that it will not hamper the analysis. It is to
be noted that for the purpose of illustration and a better
understanding, the thickness of each of parts shown is different
from the actual dimension.
[0027] In the pretreatment in which the sample retainer 5 is
employed, a liquid sample 1 is dispensed dropwise onto the liquid
absorption element 4 as shown in FIG. 2. At this time, since the
hydrophobic film 3 is present beneath and around the liquid
absorption element 4, the liquid sample 1 does not penetrate
beneath and around it from the liquid absorption element 4 and can
be dispensed dropwise within the range of 200 to 600 .mu.l by the
utilization of a surface tension. By drying the sample retainer 5
onto which the liquid sample 1 has been dispensed dropwise,
contents of the liquid sample 1 can be absorbed and retained on the
liquid absorption element 4. As a result thereof, the appearance is
similar to that shown in FIG. 1 prior to the liquid sample 1 being
dispensed dropwise. X-ray fluorescence analysis is carried out by
irradiating an area of the liquid absorption element 4 on the
sample retainer 5 in this condition with primary X-rays (the
placement of the sample retainer 5 on a sample stage of the X-ray
fluorescence spectrometer being described later).
[0028] FIG. 4 illustrates the qualitative spectrum resulting from
the analysis when in the conventional filter paper drop method the
amount of the liquid sample dispensed dropwise is chosen to be the
upper limit of 100 .mu.l, superimposed with the qualitative
spectrum resulting from the analysis based on the pretreatment, in
which using the sample retainer shown and described in this
embodiment the amount of the liquid sample dispensed dropwise is
chosen to be 500 .mu.l. According to the graph of FIG. 4, when the
sample retainer according to this embodiment is used, it is clear
that the background can be reduced down to a value equal to or
smaller than half that exhibited when the conventional filter paper
is used and, at the same time, a higher intensity of fluorescent
X-rays can be obtained.
[0029] Also, limits of detection of various elements, when using
the sample retainer according to this embodiment the amount of the
liquid sample dispensed dropwise is chosen to be 500 .mu.l are
tabulated in Table 1 below.
1TABLE 1 unit: ppb Detection Elements Limit Elements Detection
Limit B 30 ppm Zn 18 F 1 ppm As 16 Na 76 Se 24 P 56 Sr 25 K 12 Mo
27 V 34 Ag 152 Cr 26 Cd 182 Mn 16 Sn 40 Fe 18 Sb 43 Co 17 Ba 105 Ni
20 Tl 81 Cu 19 Pb 76
[0030] Considering that with the conventional filter peper drop
method in which the background is large and the amount of the
liquid sample that can be dispensed dropwise is limited to about a
value within the range of 50 to 100 .mu.l, the detection limit is
limited to a few hundred ppb in the case of a metallic element, a
relatively favorable value, it will readily be understood that with
the sample retainer according to this embodiment, the detection
limit can be improved substantially in the order of a single digit.
Also, comparing the values shown in Table 1 with those shown in
Table 1 of the previously mentioned Japanese Laid-open Patent
Publication No. 2003-90810, although the detection limit is rather
low with chromium, the detection limit with the other elements has
shown a favorable value.
[0031] As discussed above, with the sample retainer for X-ray
fluorescence analysis according to this embodiment, in the first
place, since the hydrophobic film 3 and the liquid absorption
element 4, which are irradiated with the primary X-rays, are
sufficiently thin, the background can be suppressed with the
scattered X-rays reduced. On the other hand, since with the liquid
absorption element 4 of a proper thickness pasted to the
hydrophobic film 3, a sufficient amount of the liquid sample 1 can
be retained and can be condensed uniformly, it is possible to
generate uniformly a high intensity of fluorescent X-rays.
Accordingly, the detection limit can be improved
satisfactorily.
[0032] It is to be noted that the liquid absorption element 4 is
held under a predetermined tension at all times when pasted to the
hydrophobic film 3 and, therefore, where the amount of the contents
is, for example, extremely minute, they can be uniformly and stably
retained even though dropwise dispensing and drying are repeated to
concentrate the contents in a large quantity. Also, although with
the conventional vapor deposited film of a small surface area the
contents cannot be easily concentrated sufficiently uniformly
because of crystallization, the holder according to this embodiment
allows the contents to be sufficiently uniformly concentrated owing
to the sheet-like liquid absorption element 4 having a proper
thickness and surface area and, therefore, a sufficiently stable
quantitative analysis is possible with such light elements as B, F,
Na and P.
[0033] In the next place, the X-ray fluorescence analyzing method
according to a second embodiment of the present invention will be
described. A X-ray fluorescence spectrometer used in this analyzing
method is a third embodiment of the present invention and utilizes,
as shown in FIG. 5, the sample retainer 5 for X-ray fluorescence
analysis according to the first embodiment and includes a sample
stage 16, which is the sample mount on which the sample retainer 5
is placed directly or through a sample holder 13, an X-ray source
14 such as, for example, an X-ray tube for irradiating the area of
the liquid absorption element 4, where the contents of the liquid
sample 1 (FIG. 3) is retained after the liquid sample 1 (FIG. 3)
has been dispensed dropwise and subsequently dried, and a detecting
device 15 such as, for example, an X-ray detector for measuring the
intensity of secondary X-rays 25 such as, for example, fluorescent
X-rays emitted from that area of the liquid absorption element
4.
[0034] The X-ray fluorescence analyzing method according to the
second embodiment, in which the above described spectrometer is
utilized, is a method in which the sample retainer 5 for X-ray
fluorescence analysis according to the first embodiment is used and
includes, as described previously, retaining the contents of the
liquid sample 1 (FIG. 3) by dispensing dropwise onto and then
drying the liquid sample 1 (FIG. 3) on the liquid absorption
element 4 (FIG. 3), placing the sample retainer 5 in its entirety
after this pretreatment on an opening of the cylindrical sample
holder (hollow cup) 13 made of Al or Ti and having a bottom closed,
and placing the sample holder 13 on the sample stage 16.
[0035] The objective of use of such sample holder 13 is to reduce
the background by causing anything to be not positioned in the
vicinity of the backside of the transmitting portion 3b of the
hydrophobic film and, also, to reduce the influence which may be
brought about by scattered X-rays of the primary X-rays 24 having
penetrated through to the backside of the transmitting portion 3b,
at an inner surface of the spectrometer. The sample holder 13 may
be merely in the form of an open-ended cylinder.
[0036] Also, as shown in FIG. 6, where the sample stage 16 is
provided with a through-hole 16a of a size about equal to that of
an opening in the pedestal 2, the sample retainer 5 can be placed
directly on the sample stage 16 with no sample holder used.
[0037] While the foregoing applies to so-called downward
irradiation in which the primary X-rays irradiate the sample from
above, in the case of so-called upward irradiation in which the
primary X-rays irradiate the sample from below, as shown in FIG. 7
the sample retainer 5 can be placed on the sample stage 16 while
oriented downwardly since the sample stage 16 is provided with the
through-hole 16a through which the primary X-rays 24 pass, and the
hollow cup 13 can be capped from above so as to orient downwardly
in order to reduce the influence brought about by the scattered
X-rays. Also, where as the sample mount a sample turret capable of
rotating to transport the sample to an analyzing position where the
sample is irradiated with the primary X-rays, as shown in FIG. 8,
the sample retainer 5 may be inserted into a cylindrical sample
holder (support cup) 17, which is closed at one end and has a hole
17a defined at the bottom thereof and also has a lower outer
peripheral portion reduced in diameter, with the liquid absorption
element 4 oriented downwardly, and the sample holder 17 may then be
placed on the sample turret 16 with the reduced diameter portion
thereof engaged in the through-hole 16a defined in the sample
turret 16 and having a diameter about equal to that of the reduced
diameter portion.
[0038] As hereinbefore described, by irradiating the area of the
liquid absorption element of the sample retainer 5, placed on the
sample mount 16, with the primary X-rays, the intensity of the
secondary X-rays generated is measured.
[0039] With the method and spectrometer according to the second and
third embodiments, respectively, since the sample retainer 5 for
X-ray fluorescence analysis according to the first embodiment is
used, functions and effects similar to those afforded by the first
embodiment can be obtained.
* * * * *